X-ray Pulsations from the Central Source in Puppis A

There are several supernova remnants which contain unresolved X-ray sources close to their centers, presumably radio-quiet neutron stars. To prove that these objects are indeed neutron stars, to understand the origin of their X-ray radiation, and to explain why they are radio-quiet, one should know their periods and period derivatives. We searched for pulsations of the X-ray flux from the radio-quiet neutron star candidate RX J0822-4300 near the center of the Puppis A supernova remnant observed with the ROSAT PSPC and HRI. A standard timing analysis of the separate PSPC and HRI data sets does not allow one to detect the periodicity unequivocally. However, a thorough analysis of the two observations separated by 4.56 yr enabled us to find a statistically significant period $P\simeq 75.3$ ms and its derivative $\dot{P}\simeq 1.49\times 10^{-13}$ s s$^{-1}$. The corresponding characteristic parameters of the neutron star, age $\tau=P/(2\dot{P})=8.0$ kyr, magnetic field $B=3.4\times 10^{12}$ G, and rotational energy loss $\dot{E}=1.4\times 10^{37}$ erg s$^{-1}$, are typical for young radio pulsars. Since the X-ray radiation has a thermal-like spectrum, its pulsations may be due to a nonuniform temperature distribution over the neutron star surface caused by anisotropy of the heat conduction in the strongly magnetized crust.Comment: 9 pages, 2 postscript figures, to appear in ApJ Letters; an acknowledgment is adde

Observations of cooling neutron stars

Observations of cooling neutron stars allow to measure photospheric radii and to constrain the equation of state of nuclear matter at high densities. In this paper we concentrate on neutron stars, which show thermal (photospheric) X-ray emission and have measured distances. After a short summary of the radio pulsars falling into this category we review the observational data of the 7 radio quiet isolated neutron stars discovered by ROSAT which have been studied in detail by Chandra, XMM-Newton and optical observations. Their spectra show blackbody temperatures between 0.5 and 1 million Kelvin and an optical excess of a factor of 5-10 over the extrapolation of the X-ray spectrum. Four of these sources show periodicities between 3.45 and 11.37 s, indicating slow rotation. The pulsed fractions are small, between 6 and 18 %. The magnetic fields derived from spin down and/or possible proton cyclotron lines are of the order 10$^{13}-10^{14}$ G. We then discuss RX J1856.5-3754 in detail and suggest that the remarkable absence of any line features in its X-ray spectrum is due to effects of strong magnetic fields ($\sim 10^{13}$ G). Assuming blackbody emission to fit the optical and X-ray spectrum we derive a conservative lower limit of the ``apparent'' neutron star radius of 16.5 km $\times$ (d/117 pc). This corresponds to the radius for the ``true'' radius of 14 km for a 1.4 M$_{\odot}$ neutron star, indicating a stiff equation of state at high densities. A comparison of the result with mass-radius relations shows that in this case a quark star or a neutron star with a quark matter core can be ruled out with high confidence.Comment: 15 pages, 5 figures, to appear in ASI proceedings of The Electromagnetic Spectrum of Neutron Stars, Marmaris 2004, very minor revisio

Abusive Head Trauma and Mortality-An Analysis From an International Comparative Effectiveness Study of Children With Severe Traumatic Brain Injury

Objectives: Small series have suggested that outcomes after abusive head trauma are less favorable than after other injury mechanisms. We sought to determine the impact of abusive head trauma on mortality and identify factors that differentiate children with abusive head trauma from those with traumatic brain injury from other mechanisms. Design: First 200 subjects from the Approaches and Decisions in Acute Pediatric Traumatic Brain Injury Trial—a comparative effectiveness study using an observational, cohort study design. Setting: PICUs in tertiary children’s hospitals in United States and abroad. Patients: Consecutive children (age < 18 yr) with severe traumatic brain injury (Glasgow Coma Scale ≤ 8; intracranial pressure monitoring). Interventions: None. Measurements and Main Results: Demographics, injury-related scores, prehospital, and resuscitation events were analyzed. Children were dichotomized based on likelihood of abusive head trauma. A total of 190 children were included (n = 35 with abusive head trauma). Abusive head trauma subjects were younger (1.87 ± 0.32 vs 9.23 ± 0.39 yr; p < 0.001) and a greater proportion were female (54.3% vs 34.8%; p = 0.032). Abusive head trauma were more likely to 1) be transported from home (60.0% vs 33.5%; p < 0.001), 2) have apnea (34.3% vs 12.3%; p = 0.002), and 3) have seizures (28.6% vs 7.7%; p < 0.001) during prehospital care. Abusive head trauma had a higher prevalence of seizures during resuscitation (31.4 vs 9.7%; p = 0.002). After adjusting for covariates, there was no difference in mortality (abusive head trauma, 25.7% vs nonabusive head trauma, 18.7%; hazard ratio, 1.758; p = 0.60). A similar proportion died due to refractory intracranial hypertension in each group (abusive head trauma, 66.7% vs nonabusive head trauma, 69.0%). Conclusions: In this large, multicenter series, children with abusive head trauma had differences in prehospital and in-hospital secondary injuries which could have therapeutic implications. Unlike other traumatic brain injury populations in children, female predominance was seen in abusive head trauma in our cohort. Similar mortality rates and refractory intracranial pressure deaths suggest that children with severe abusive head trauma may benefit from therapies including invasive monitoring and adherence to evidence-based guidelines

Weighing the Giants - I. Weak-lensing masses for 51 massive galaxy clusters: project overview, data analysis methods and cluster images

This is the first in a series of papers in which we measure accurate weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at redshifts 0.15<z<0.7, in order to calibrate X-ray and other mass proxies for cosmological cluster experiments. The primary aim is to improve the absolute mass calibration of cluster observables, currently the dominant systematic uncertainty for cluster count experiments. Key elements of this work are the rigorous quantification of systematic uncertainties, high-quality data reduction and photometric calibration, and the "blind" nature of the analysis to avoid confirmation bias. Our target clusters are drawn from RASS X-ray catalogs, and provide a versatile calibration sample for many aspects of cluster cosmology. We have acquired wide-field, high-quality imaging using the Subaru and CFHT telescopes for all 51 clusters, in at least three bands per cluster. For a subset of 27 clusters, we have data in at least five bands, allowing accurate photo-z estimates of lensed galaxies. In this paper, we describe the cluster sample and observations, and detail the processing of the SuprimeCam data to yield high-quality images suitable for robust weak-lensing shape measurements and precision photometry. For each cluster, we present wide-field color optical images and maps of the weak-lensing mass distribution, the optical light distribution, and the X-ray emission, providing insights into the large-scale structure in which the clusters are embedded. We measure the offsets between X-ray centroids and Brightest Cluster Galaxies in the clusters, finding these to be small in general, with a median of 20kpc. For offsets <100kpc, weak-lensing mass measurements centered on the BCGs agree well with values determined relative to the X-ray centroids; miscentering is therefore not a significant source of systematic uncertainty for our mass measurements. [abridged]Comment: 26 pages, 19 figures (Appendix C not included). Accepted after minor revisio

Expulsion of Magnetic Flux Lines from the Growing Superconducting Core of a Magnetized Quark Star

The expulsion of magnetic flux lines from a growing superconducting core of a quark star has been investigated. The idea of impurity diffusion in molten alloys and an identical mechanism of baryon number transport from hot quark-gluon-plasma phase to hadronic phase during quark-hadron phase transition in the early universe, micro-second after big bang has been used. The possibility of Mullins-Sekerka normal-superconducting interface instability has also been studied.Comment: Thoroughly revised version. Accepted for Astrophysics & Space Scienc